This invention relates to probe-like electrical heater devices, and more particularly to such devices which are intended for use in pollution control systems, such as those employing zirconia oxygen sensors or titanium dioxide sensors as used with internal combustion engines where the environment involves relatively strong, vibratory forces which are likely to be generated by the engines.
In the past, probe-like electrical heater devices have been utilized in various situations, to bring concentrated heat to a small area. One well-known use of such heater devices is in electrical cigar lighters, where a plug-like ignitor unit has at its inner end a spiral heating coil that is arranged to contact and ignite the end of a cigar or cigarette. Although a certain amount of vibration was involved in such use, the disruptive forces were usually not sufficiently severe to warrant extreme measures to combat them.
In a somewhat lesser degree, the same is true of ignitor or glow plugs as utilized in the combustion chambers of diesel engines and the like.
With the advent of increased automobile use and a greater awareness of environmental pollution, new control devices are being considered to monitor the exhaust gases of internal combustion engines. One such device is the zirconia oxygen sensor, and another is the titanium dioxide sensor, both of which involve a probe-like electrical heating coil assemblage that is subjected to the flow of oxygen and/or other gases. Sensors such as these are associated with automobile exhaust systems, where strong vibrations are likely to occur. Previously produced probe-like electrical heaters as tested in this environment have not had a satisfactory, useful life. The continuous heating of the resistance coil in its electrically energized condition has contributed to coil failures while other components of the devices remained operative. Also, prior devices were found to be too slow in heating.